Revertive call circuits



June 9, 1953 F. A. MORRIS 2,641,652

REVERTIVE CALL CIRCUITS Original Filed April 23, 1947 16 Sheets-Sheet 1 I N VEN TOR. FRANK A. MORRIS A F TOR/V5 Y June 9,

Original F. A. MORRIS Filed April 25, 1947 FIG. F/G'. FIG. FIG. FIG. ['76. FIG. 4. 5. 6. Z 6. 9. l0.

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IN V EN TOR. FRANK A. MORRIS A T TORNE Y June 9, 1953 F. A. MORRIS REVERTIVE CALL CIRCUITS Original Filed April 25, 1947 16 Sheets-Sheet 4 INVENTOR. FRANK A. MORRIS ATTORNEY F. A. MORRIS REVERTIVE CALL CIRCUITS Original Filed April 23, 1947 June 9, I 1953 16 Sheets-$heet 5 NR8 husk INVENTOR. FRANKA'MURR/S SEE/7613. Y

JTTORIVEY June 9, 1953 F. A. Mofikls REVERTIVE CALL CIRCUITS Original Filed April 25, 1947 16 Sheets-Sheet 6 INVENTOR. FRANK A. MORRIS 555 FIG. 14

ATTORNEY June 9, 1953 F. MORRIS 2,641,652

REVERTIVE CALL CIRCUITS,

Original Filed April 23, 1947 16 Sheets-Sheet 7 CC CZ CD C'X CXD CY, CYD CX C67 CY CTH INVEN TOR. FRANK A. MORRIS A TTORNEY June 9, 1953 F. A. MORRIS 2,541,652

REVERTIVE CALL cmcuns Original Filed April 23, 1947 16 Sheets-Sheet 8 I l I l 7O COA/MCTS RELAYS 57 AM 87/ 2 (FIG. /4.)

[ 7 9 INVENTOR.

FRANK A. MORRIS A TTORNEY F. A. mofims REVERTIVE CALL CIRCUITS Original Filed April 2?, 1947 June 9, 1953 16 Sheets-Sheet 9 ALB INVENTOR. FRANK AMORR/S ATTORNEY June 9, 1953 F. A. MORRIS 2,641,652

' REVERTIVE CALL CIRCUITS Original Filed April 23, 1947 l6 Sheets-Sheet 1O SEEP/6.4. ALS .APA AA A52 A8! AP) I i n r '6 I I I I I I I I I ATTORNEY June 9, 1953 F. A. MORRIS REVERTIVE CALL CIRCUITS Original Filed April 23, 1947 16 Sheets-Sheet l2 41 ,4 ALs SEEP/66.

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June 9, 1953 F. A. MORRIS 2,641,652

REVERTIVE CALL CIRCUITS Original Filed April 25, 1947 16 Sheets-Sheet 1s 70 XX BANKS 0/ F/IVDE/F 641 /7 CH 65w. (FIG. 4JAND BCAS JCAP 678 nvmvrox. 1761/4 FRANKA.'MORRI$ A TTORNE Y l Sheets-Shet 14 INVENTOR. FRAIVKA. MORRIS ATTORNEY I F A MORRIS REVERTIVE CALL CIRCUITS- fia/fi x2 0 uwl June 9, 1953 Original Filed April 23, 1947 RMB June 9, 1953 r-. A. MORRIS REVERTIVE CALL CIRCUITS Original Filed April 25, 1947 16 Sheets-Sheet 15.

IN V EN TOR. FRANK A'MORR/S 7o FREQUENCY GENEPA ms ATTORNEY Patented June 9, 1953 REVERTIVE CALL CIRCUITS Frank A. Morris, Rochester, N. Y., assignor to Stromberg-Carlson New York Company, a corporation of Original application April 23, 1947, Serial No. 743,415. Divided and this application June 21, 1949, Serial No. 100,373

1 The present invention relates to telephone systems and more particularly to reverting call party line circuits for use in automatic telephone systems. i V a This is a division of United States Patent. No. 2,567,650, issued September 11, 1951, the invention covered thereby being assigned to the same assignee as the invention described therein. I It is an object of my invention to provide a new and improved multi-party telephone system incorporating new and improved reverting call circuits.

GENERAL DESCRIPTION In accordance with my invention,'thereis provided a system employing step-by-step switches for line finding, each line finder being directly associated with a selector to form'a finder-selec tor link or combination.- There is illustrated herein a 1000-line system and there is provided a suitable number of finder-selectorlinkaas twenty, for example. There is provided an allotting circuit for pre-selecting an idle link for the next initiated call. rate of handling calls, the allotter has duplicate relays for all functions, thereby constituting a dual allotter in which each half is normally brought into action by half of the lines, there being, for example, 50 lines assigned to each allotter. Provision is made for transferring all the lines to one-half of the allotter under oer-- tain conditions.

h After the line finder-selector link has selected; the calling line, the selector is caused to hunt,

upon the dialing of the first digit of the called number, to select an idle connector in that group of connectors designated by the first digit. After selection of the connector, second and third digits are transmitted to cause the connector step-by-step switch to move to a position corresponding to the called subscriber.

Line circuit.-In connection with a system such as that described herein, there is provided is so arranged; to prevent the indefinite holding.

of a line finder and selector combination when a permanent fault appears by disassociating or locking out the faulty line from the switching In order to increase the 1 3 Claims. (Cl. 179-17) equipment after a period of time determined by common timing equipment; and also to eliminate the line, start and marking grounds on terminat-' ing calls in order to prevent the unnecessary use of the line finder-selector links.

Line finder.The line finder, as indicated above, is employed to find the calling line. In addition to this primary function, the line finder is used to attach the tip and ring conductors or leads to the calling line; to conduct a busy test to prevent cutting through metallic connections if a connector has seized the calling line during the-process of line'finding; to cut tip and ring conductors through to the connector on a metallic basis if the busy test is successful; to recycle the allotter if the line finder fails to stop in either direction of motion of the step-by-step switch; to provide trunk call. identification to' succeeding circuits; and to provide direct control of all links busy and link test marking paths to the allotter. The line finder may be provided with means for discriminating restricted calling" levels and timed calling levels. 1

AZZotter.-The dual allotter, as stated above, serves primarily to control the operation of a pro-selected line finder and to pre-select another idle link upon completion of a line finding op eration. Theallotter is also used to pre-rimpulse the selector associated with the idle line finder when the allotter is energized; to drive the line finder in whatever direction is necessary to at-Q tach the finder-selector link to the calling line; to drive the line finder in one direction only to attach the linkto a calling trunk as distinguished from a calling subsc'ribersline; to recycle if the line or trunk is not found within a prescribed time; to transfer functions so that one side of the allotter can carry the entire load of the line group in case of trouble or in case all links normally served by the other side become busy; to operate peg count meters; and to return the all links busy tone when required.

SeZector.Thepurpose of the selector circuit, as indicated previously, is to select a group of connectors under the direction of the dial and hunt automatically-for an idle trunk in that group. In order to accomplish itspurpose, the

selector is caused to repeat the dial pulses received from the calling party in order to select the desired group of connectors, to hunt in the selected group for an idle trunk in the level se lected by the dial, and then to establish a connection to the succeeding switching equipment. There may also be provided provisions for digit canceling, digit adding,'permanent time release 3 and the transmission of link idle and link busy indications to the allotter.

Connector.The primary functions of the connector are to select a subscriber line and to establish ringing of the desired called station under the control of the calling party. The connector may be of various types depending upon the kind of service which it may be called upon to perform, such as party line ringing of either the harmonic or code type, P.B.X trunk hunting, conversation timing from one or both ends of the system, and revertive calling.

P.B.X trunk hunting allows the assignment of successive numbers to a business establishment, or the like, whose telephone needs are sufficiently great to justify the assignment of two or more consecutive telephone lines, in which case, the connector tests the lines in succession until a free line is found. Normally, when the first line is called, testin begins over the entire group. Provision may be made, as for night service, for example, such that if any line other than the first in the group is called, that line only is tested. This feature allows the listing in the telephone directory of all telephone lines, except the first, as night lines for particular individuals whereby at such times they receive the benefit of individual line service.

Further objects and advantages as well as a detailed understanding of my invention will be apparent from a study of the following description when read in connection with the drawings in which Fig. 1 illustrates the basic features-of a step-by-step switch which may be'used to carry out the principles of my invention, Fig. 2 is a chart showing the relationship of the various figures of the drawings and which enables a complete wiring diagram to be assembled if the various figures of the drawings are placed in the indicated locations, Fig. 3 illustrates the line circuit of my system, Fig. 4 depicts the finder switch and associated circuits, Figs. 5 and 6 illustrate the various component parts of a selector embodying the principles of my invention, Figs. 7 and 8 and 9 show a connector circuit illustrating the principles of my invention, Fig. 10 shows a terminating line circuit, Figs. ll, 12 and 13 illustrate a dual allotter for use in the system described herein, Fig. 14 illustrates equipment which is common to thesystem, Figs. 15 and 16 illustrate an alter-v native reverting call circuit and Figs. 17 and 18 illustrate modifications of features of the circuits shown in Figs. 4, 11 and 12 and Figs, 7, 8 and 9 respectively.

, With respect to Figs. 5 and 6 relating to the selector, it is desired to point out that if permanent timing lock-out is to be employed, the equipment within the dashed rectangle marked with the numeral B is used, but if the look-out feature is not desired, the ground connection indicated within the dotted rectangle C is substituted. Attention is also called to the dashed rectangle D which is used if digit adding functions are required, in which case wiring M is used. If digit adding is not employed, rectangle D is omitted and wiring N is substituted.

Referring to the connector, illustrated in Figs. 7, 8, and 9, a number of alternative provisions are made. If directory number revertive calling is employed, the apparatus shown within the dashed rectangle E and D," W, and X wiring is used, but if the special revertive call circuit illustrated in Figs. 15 and 16 is furnished, the parts shown within rectangle E are omitted and D, W and Y wiring is used. If the trunk huntlng feature is utilized, the parts shown in rectangle F are included and wiring C is used instead of D. If dual timing is made part of the system, wiring D is used, but if this service is not provided, wiring W is used.

Step-by-step switch It is believed that a complete understanding of the principles of my invention requires not only an explanation of a complete telephone system, but also a description of a suitable step-by-step switch. There is illustrated in Fig. l, a switch specially adapted, for use in the system embodying my invention and known by the trade name XY switch. This switch derives its name from the fact'that the wipers or contact brushes, during movement to a desiredposition, traverse first in a primary direction and then in the same plane but in a secondary direction at right angles to the first direction, which, in the right-hand rectangular co-ordinate system are X and Y directions, respectively.

There is provided a carriagel, which makes the primary and secondary stepping movements and has a set of contact brushes comprising two pairs of wipers 2 and 3 mounted on it for tip, ring. sleeve and hunt connections, respectively. These wipers are bifurcated, employing twin contacts that make connection directly onto bare wires which run in banks behind the switches. The bare wires may be arranged in molded frames which may be rigidly mounted to the cells which in turn hold the switches.

The carriage is driven by the cog roller or tubular shaft assembly 4 which slides along, the shaft 5 during the X motion. The cog roller 4 is shown in theform of a double-cut tubulargear with ratchet teeth out parallel to its length and rack teeth out as rings. The annular rack teeth mesh with and are driven in the X motion by a suitable sprocket or gear 6. For stepping in the X direction, the X magnet 1, located in the upper left corner of the plate 8, operates, through a pawl 9, the ratchet wheel Iii which. is suitably mounted on the sprocket assembly. In response to repeated pulses the magnet: steps the cog. roller assembly 4 along the shaft 5, positioning the wipers on the carriage l successively before each wire bank. Since four wipers are involved and each wiper has its own set of 11 wires, 44 rows of wires each 11 deep are lined up along the front edge of the mechanism plate, immediately before the Wipers v(see Fig. 4). The eleven pairs of wires that are lined up before a pair of wipers constitute a Wire bank.

The XY switch, is nominally a 100 point switch, i. e., is normally given ten steps in the X direction and ten steps in the, Y direction, thereby making possible the selection by the Wipers, of any one of 100 lines.

To mark the level of X travel, for finder operation, timing or discriminator purposes, an auxiliary set of contact brushesadapted to be positioned according to the position of the primary movement or set of brushes, another pair of wipers indicated by the numerals II and Ha enters a separate bank comprising X and XX levels. Wipers ll and Ha are operated by a pinion l2 assembled with the sprocket B through a rack l3 to which it is attached. Thus, as the X magnet steps the sprocket 6, both the cog roller 4 and wiper rack move, ,roller 4 to the right and rack l3 upwardly, as viewed in the drawing.

When the X wiper I i has found the proper level,

thereby positioning the Wipers on the carriage before the proper wire banks, the X magnet 'lis' de-energized and the Y magnet l5. takes over.

The Y magnet. i5 is located. in the lower'central portion of the. mechanism plate. In stepping, its pawl It operates directly on the ratchet teeth of the cog roller 4, turning it, and thus driving the wipers 2 and 3 into the wire banks through the interaction between rack and pinion 2|.

The. X position of the wipers is shown by reference to a scale I! attached to the mechanism plate and the Y position by reference to a numbered drum l8 located on the tubular shaft assembly. Thus, the position of the wipers is determined directly and quickly. 1

Itshould be recognized that the momentum of the switch, if not arrested, would carry each step beyond its limits. This is more easily realized when one considers that the stepping is of the order of fifty per second. vIn order to stop the X motion at each step, the end of the armature 35 of the X magnet engages atooth of the sprocket at the bottom pointof the armature travel. The sprocket motion is, therefore, locked each time the X magnet completes a pulse.

In the Y motion, a cani- (not shown) on. the underside of the Y armature operates against a member 22 called the stop bar. This stop bar is rocked forward at each downward stroke of the Y armature. A knife edge on the stop bar 22 engages a ratchet wheel 23 on the end of the cog roller 4 locking the rotation of the cog roller, and

thus the advancement of the Wipers, at the completion of each Y armature stroke.

There are provided X off-normal contacts or switches 25, Y off-normal contacts or switches 26, over-flow contacts or switches 21 and a release switch 28.

The off-normal and: overflow switches are mounted as a common assembly located in the lower left-hand corner of the mechanism plate and the release springs are mounted on a separate assembly located near the release magnet The X and Y off-normal springs 25 and 26, respectively, perform similar functions, that of informing the relayequipm'ent associated with each switch as to the position of the brushes or wipers. Operation of the X off-normals, for instance, indicates that the switch has taken at least a single step in the X direction. Operation of the Y off-normals similarly indicates that at least a single step has been taken in the Y direction.

The circuit function of the off-normals differs in each use of the switch'but, in general, indi cates that it has either moved in one direction and should now move in another or all necessary motion has taken place.' There is, however, one circuit function common to all switches and that is to remove current from the release magnet when the brushes have returned to the normal position. When the release signal is given, current is kept on the release magnet 30 until theswitch is fully home and is then removed to' avoid unnecessary current flow and heating. Both the X and Y off normals are used in this function since the switch can be moved independently in either direction. j 1 In the event of certain incorrect manipulations or an all-trunks-busy condition, hunting switches may progress the entire length of the bank without encountering a stepping signal. Unless some means of correction were provided, they would continue to hunt vainly until the circuit was tie-energized. Overflow springs 21, arranged to operate in the extreme position of the brushes in either the X or Y directions (namely the eleventh The release springs 28 have two important functions in connection with the release. of the switch. First, it. is. necessary to. continue the re,-

lease signal until the switch is fully home. despite any re-energization of the circuit which might occur- Second, there. must be positive protection against premature seizure of a switch before it. is fullyhome. .In. the XY switch, the first is accomplished by a release spring contact establish? ing a self-locking electrical circuit which keeps the driving pawls 9 and l6"removed from the ratchet wheel (X motion) and the .cog roller (Y motion)- The lock is interrupted when the switch returns home. The second function is performed by a seoond'release springwhich maina tainsa busy indication until the switch ishome, thus preventing its seizure until 'everythingis normal. When the release magnet 30 is ener gized, stop members. 3! and 32 are removed from engagement with cog roller 4 and sprocket l0, respectively, through operation of armature 33.

The Y return movement of the carriage is then performed by a spring 34 coiled in the tubular shaft of the cogroller and the X movement by a. spring (not'shown) coiled a round the shaft of the sprocket'fi.

DETAILED CIRCUIT DESCRIPTION In the following: description, at callis traced. from-:the calling partys. station to the called party's station. Revertive calling is then 'discussed and finally circuit; refinements to provide special features and. to take" account ofspecial conditions are described.

The. telephone system herein described in detail comprises a single selector and, therefore, serves:

a lOQll-line system and requires the transmission of four digits, one to select the desired group of: connectors, the second to determine the tens digit of the called number, the third to select the units digit of the called number, and the fourth to ring the called line. The principles of my invention, of course, are not limited to the particular choice of circuits described herein as a system and. my invention'is equally applicable to any desired combination of the various circuit components.

In describing the circuits involved, the various relays are designated by letter combinations. The. first: letter indicates the part of the system in. which the. relay is located, i. e., L indicates line circuit, F indicates finder, A- indicates allotter, S indicator selector, C indicates connector, R indi cates a special reverting call circuit and B refers to common-equipment. Following the initial letterare one or more letters'which are usually the initials of the name of the relay with which they are associated and which serve to identify that relay. For example, C refers to a calling relay, PT to a permanent timing relay, D to delay, and X anclY to switch motion. Thus, SXD re fers to a slow release (delay) relay associated.

with theXmotion of the selector switch. The

energized as'lon'g as there is an idle link(a link' comprising a finder and a selector). The other relays are energized at various times during the progress of a call. Hence, in the drawings, the armatures of the ALB and ALI relays are shown in the operated positions while the armatures of the rest of the relays are shown unoperated. The term battery when used in the following circuit description refers to thenegative side of battery. The positive side of battery is grounded andhencethe term ground refers to positive battery. v

' Line circuit Referring'to Figure 3 of the drawings, a call isinitiated by removing the receiver from the hook-switch or cradle, thereby closing the hookswitch contacts 4| as shown in Fig. 3 and com pletin'g a circuit through a suitable dialing mechanism 42 to the Tip and Ring leads, T and R, respectively. Closure of the hook switch com-' pletes a circuit for the energization of line relay LL. Relay LL is a two-winding relay. One terminal of the lower winding is connected to'battery and the other terminal is connected to the ring lead R through contact LCO-l and armature LCO-3. The circuit to ground from the tip lead '1' comprises armature LCO-I, contact LCO-Z, the other coil of relay LL, contact LLO-l and armature LLO-Z to ground. If all-links-busy tone is to'be provided, the foregoing circuit is' grounded through a'transformer as indicated in dashed lines in Fig. 3 instead of directly as shown by the solid line.

Operation of line relay LL grounds a start lead-LST to the dual allotter in order to cause a pre-selected finder to hunt for the calling line, grounds the X-mark lead to mark the tens position of the calling line in the banks of the line finder switch FSw (Fig. 4) and also grounds the H lead to mark the units position of the calling line in the banks of the line finder FSw.

The X-mark circuit is as follows: ground at armatureLL-l, contact LL-2 of line relay LL, armature LL04, and contact LLO-E of lockout relayLLO to the contact in the X bank of the line finder switch FSw corresponding to the calling line. The hunt lead H is grounded as follows: ground at armature LL-S, contact LL-d, armature LLO-H, and contact LLO-I2, to .the contact in the hunt bank ofthe line finder corresponding to the calling line. 7

Ground on the start lead is utilized to operate a start relay in the allotter (Figs. l1, l2 and 13) which initiates the energization of the line finder switch (Fig. 4) chosen by the allotter to serve the call. The start lead is traced over. the following; circuit: ground at armature LL-I, contact LL-Z, armature LLO- l, contact LLO-5, resistor 43,"and start lead LST, to the allotter.

When the calling line is found, as will be more fully described hereinafter, ground is placed on the sleeve lead S inthe sleeve bank of the finder switch FSw (Fig. l) and conducted to the line circuit by lead S. Presence of ground on the sleeve lead S operates the cut-oiT relay 'LCO over a circuit extending from grounded sleeve-lead S, armature LLO-B, contact LLO-B, winding of cutofi relay LCO to battery. If provision is made for the transmission of coin box tone to an operator, the cut-off relay LCD is connected to battery through atransformer winding as indicated in dotted lines in Fig. 3 instead of directly as shown by the solid line. Cut-on relay LCO locks up through a circuit extending from grounded sleeve locked up as explained above.

, tacts in the line finder and the selector.

lead S, through contact LCO -9, armature LCD- 8,

' and winding of relay LCO to battery. Opera- LOO-5 and armature LOO-6 to one terminal of the winding of rela LLO. The other terminal of the LLO coil is connected to battery. Operation of the lock-out relay LLO breaks the original energization path to the cut-off relay LC'O at contact LLO-9 but the cut-off relay LCO remains Lock-out relay LLO locks up to the grounded sleeve lead S through its own armature LLO-B- and contact LLO-I and hence is independent of any subsequent action of cut-off relay LCO;

Allotter and line finder In the at rest condition of the allotter, i. e., circuits connected but no calls being made, the allotter is cut through to an idle link comprising an interconnected finder and selector by means of contacts and brushes of the rotary link selector switch ALS. The link busy relays ALB and ALB associated with left and right hand portions, respectively, of the allotter and the link idle relays ALT and ALI are normally picked up by grounds derived through chains of con-' Thus, referring to relay ALB (see Fig. 12), one side of its winding or coil is connected to battery. The other side of the coil ALB is connected to ground over a circuit extending through contact DK-! and arm DK-2 of the disable key DK, armature A'S2-l8 and contact AS2-I9 of start relay ASZ, ALB lead to the finder (Fig. l) armature FY orb-3 and contact FYon-4 of the finder Y oiT-normal switch "FYon, contacts of the make busy switch FMB, ALB lead from the finder to the selector (see Figs. 5- and 6), armature SYon-l and contact SYOn-2 of the selector Y ofi-normal switch SYon, conductor 36, contact 504 and armature SD- l of selector delay relay SD, and contacts of the selector make busy switch SMB to ground. Inasmuch 'as all finder-selector links are multi plied if any link is not operated or employed, relay ALB is energized through at least one closed off-normal contact in the finder and'the selector. The operating circuit for linkidle relay- ALI is as follows: battery, upper winding of ALI, armature APT-l and contact APT-2 of the Permanent Timing relay APT, armature AS2-4,

contact AS2-3, arm and contact of rotary switch 

